A machine head (also referred to as a tuner, or gear head) is part of a string instrument ranging from guitars to double basses, a geared apparatus for applying tension and thereby tuning a string, usually located at the headstock. A headstock has several machine heads, one per string. Non-geared tuning devices as used on violins, violas, cellos, lutes and (formerly) Flamenco guitars and ukuleles are known as tuning pegs.
Contents |
Traditionally, a single machine head consists of a cylinder or capstan, mounted at the center of a pinion gear, a knob or "button" and a worm gear that links them. The capstan has a hole through the far end from the gear, and the string is made to go through that hole, and is wrapped around the capstan. To complete the string installation, the string is tightened by turning the capstan using the tuning knob. The worm gear ensures that the capstan cannot turn without a movement on the knob; it also allows precise tuning.
Banjos usually employ a different mechanism using planetary gears - in this case the knob and the capstan both rotate on the same axis. A few guitars (e.g. the original Gibson Firebird, early Gibson basses and Mario Maccaferri's plastic instruments) have used this design.
The guitarist adjusts the tension of the various strings using the knobs so that they are correctly tuned: a higher tension yields a sharper pitch, a lower tension a flatter pitch. Typical tensions for steel-string acoustic guitars with "light" tension strings are 10.5 kgf (23.3 lbf, 103 N) to 13.8 kgf (30.2 lbf, 135 N).
Normally, worm gears provide a gear ratio of 14:1, though versions with 18:1 gear ratio also exist. They provide better accuracy in fine tuning, though are somewhat slower for initial string winding.
Several kinds of machine head apparatus exist:
Since 1950s, guitar performance techniques evolved, and aggressive usage of tremolo arm became widespread. However, the original machine heads couldn't withstand the rigors of constant string tension changing, and strings got out of tune after using tremolo several times. Several manufacturers, including Grover and Floyd Rose, introduced a new design, commonly named locking machine heads nowadays: a machine head with additional mechanism to lock it in place and stabilize tuning while playing and using tremolo. However, such machine heads reached limited success, mostly because of their price: as of 2006[update], locking ones are about 50% more expensive than original. Many break strings when tension is increased while the mechanism is locked and later unlocked, which frequently happens in music stores.
Note that on some guitars, such as those with Floyd Rose bridge, string tuning may be also conducted using microtuning tuners located at guitar bridge. In this case, main machine heads at headstock may be missing entirely, as well as the headstock itself.
Likewise, 'headless' guitars and basses, notably those designed by Steinberger and their licensed imitations, such as the Hohner Jack Bass, and unlicensed imitations such as the Washburn Bantam, have the machine heads at the body end. Steinbergers and Hohners require specialist double-ball end strings, whereas the Washburn Bantam can take regular strings.
Several manufacturers established well-known designs of knobs and whole machine heads. These designs are subject to copy and reference:
There are several US patents on machine heads, mostly covering various aspects of locking: